This invention relates to rotary cutting tools such as reamers or the like and especially to an improved tool head construction wherein the head is formed from a single piece of specially prepared cylindrical bar stock having a composite metallurgical structure. More particularly, the invention relates to an improved means for fabricating a radially adjustable tool head such as an expansion reamer, for example, to eliminate the separate steps of machining seats for tool steel cutting elements or blades and then anchoring the tool steel blades to the machined body formed of low to medium alloy carbon steel. The invention has particular utility in connection with the fabrication of expansion reamers of the type that are provided with a threaded pin that is turned into a threaded axial bore in the body to force the blades radially outward.
Expansion reamers are normally provided with axially extending radial slots so as to permit radial expansion of the tool head when an adjusting pin is turned into a threaded axial bore in the head. The expandability of the tool makes possible the maintenance of a predetermined outside diameter while permitting necessary grinding of the outside diameter. The expansion capability is used to compensate for wear etc. and permits minor adjustment to maintain tolerances.
Rotary cutting tools such as expansion reamers and the like are conventionally formed of a generally cylindrical body of low to medium alloy carbon steel having axially extending seats machined therein to receive tool steel cutting elements or blades. The blades are usually brazed, silver soldered or welded to the body. When the blades are brazed to the body, heat from brazing excessively softens the tool steel blades because of overtempering or insufficient hardening. When blades are soldered in place, the resulting tool has a low thermal resistance and when they are welded, the resulting interface between the blades and the low carbon steel body, is brittle and vulnerable to damage from shock and vibration.
Known rotary cutting tools such as expansion reamers described above may also be provided with inserted wear resistant carbide or ceramic tips in order to increase tool life and cutting capabilities, for example. Such a carbide tipped tool results in a multi-component assembly comprising a low to medium alloy carbon steel body, tool steel blades and carbide tips. The assembly involves machining seats or slots for both the blades and the tips, and brazing or otherwise bonding all of them to the body.
Although the properties of carbide or ceramic which make them desirable in cutting tools are not adversely influenced by the heat required for brazing or bonding them to the steel body, the addition of more and diverse elements adds significantly to the manufacturing costs of this form of rotary cutting tools.
The tool of the present invention reduces, if not eliminates the disadvantages and shortcomings discussed above of known forms of rotary cutting tools and affords other features and advantages heretofore not obtainable.